The NASA COTS award was for US$171 million; Orbital Sciences expects to invest $150 million in addition, split between $130 million for the booster and $20 million for the spacecraft.[8] As of april 2012, development costs are estimated at $ 472 million.[9]

On 10 June 2008 it was announced that the Mid-Atlantic Regional Spaceport, part of the Wallops Flight Facility in Virginia, would be the primary launch site for the rocket.[10] Launch pad 0A, which is the former launch pad for the failed Conestoga rocket will be modified to handle Antares.[11] A launch from Wallops would reach the International Space Station’s orbit as effectively as from Cape Canaveral, Florida, while being less crowded.[8][12] It is currently planned for the first Cygnus flight to be an unloaded demonstration; the first Cygnus flight may or may not be the first Antares flight, pending additional bookings.

On December 10, 2009 Alliant Techsystems Inc. (ATK) test fired their Castor 30 motor for use as the second stage of the Antares rocket.[13] In March 2010 Orbital Sciences and Aerojet completed test firings of the NK-33 engines.[14]

Layout

The first stage uses RP-1 (kerosene) and liquid oxygen (LOX) as propellants, powering two NK-33-derived engines (sold by Aerojet as AJ-26 engines). As Orbital has little experience with large liquid stages and LOX propellant, some of the Antares first stage work was contracted to Yuzhnoye SDO, designers of the Zenit series. One source claims that includes “main-stage fuel tanks and associated plumbing”.[8] The core provided by Yuzhnoye includes propellant tanks, pressurization tanks, valves, sensors, feed lines, tubing, wiring and other associated hardware.[3] Like Zenit, the Antares vehicle will have a 3.90 m (154 in) diameter. It will have a 3.9 diameter payload fairing.[2]

The second stage is a solid, the Castor 30, developed by ATK as a derivative of the Castor 120 solid stage, 293.4 kilonewtons (66,000 lbf) average (395.7 kilonewtons (89,000 lbf) maximum) thrust, utilizingelectromechanicalthrust vector control.[15] The first two flights (Antares 110) will use a Castor 30A, the next two flights (Antares 120) will use an enhanced Castor 30B. The longer Castor 30XL second stage will be used on subsequent flights.[15][16]

The optional third stages planned, are the Bi-Propellant Third Stage (BTS) and a ATK Star 48-based third stage. BTS is derived from the Orbital Science’s GEOStar spacecraft bus and uses nitrogen tetroxide and hydrazine for propellant; It is intended to place payloads into a more precise orbits.[2] The Star 48-based stage uses a Star 48BV solid rocket motor and is planned to be used for higher energy orbits.[2]

This hypergolic propulsion system is planned to form the basis of the Cygnus spacecraft.[citation needed] The equipment section will likely be topped by a smaller development of the MPLM for pressurized cargo.[citation needed] Initial production of pressurized modules will take place in Italy. No reentry and return capabilities are planned. Design details are still subject to change.[8][dated info]

Scheduled launches

In April 2012, David Thompson, CEO of Orbital Sciences, stated the initial launch of Antares is expected to occur in August 2012 and the Orbital COTS Demonstration mission no sooner then October or November 2012.[17]

List only includes relatively near missions, more missions are planned than are listed below. The first digit of the version number refers to the single core first-stage, it will always be one. The second digit refers to the second-stage, 1 used for the Castor 30A, 2 for Castor 30B, and 3 for Castor 30XL. The third digit refers to the third-stage, 0 represents that no third-stage is being used, 1 represents BTS and 2 represents the Star 48-based stage.[16]